You can use
RMAN to apply incremental backups to data file image copies. With this recovery
method, you use RMAN to recover a copy of a data file—that is, you roll forward
(recover) the image copy to the specified point in time by applying the
incremental backups to the image copy. The image copy is updated with all
changes up through the SCN at which the incremental backup was taken. RMAN uses
the resulting updated data file in media recovery just as it would use a full
image copy taken at that SCN, without the overhead of performing a full image
copy of the database every day. The following are the benefits of applying
incremental backups to data file image copies:
•
You
reduce the time required for media recovery (using archive logs) because you
need to apply archive logs only since the last incremental backup.
•
You
do not need to perform a full image copy after the incremental restoration.
If the
recovery process fails during the application of the incremental backup file,
you simply restart the recovery process. RMAN automatically determines the
required incremental backup files to apply, from before the image data file
copy until the time at which you want to stop the recovery process. If there is
more than one version of an image copy recorded in the RMAN catalog, RMAN
automatically uses the latest version of the image copy. RMAN reports an error
if it cannot merge an incremental backup file with an image copy.
Performing
a Fast Switch to Image Copies
You can use
image copies of data files for fast recovery by performing the following steps:
1. Take the data file offline.
2. Use the SWITCH TO ... COPY command to
point to the image copy of the files.
3. Recover the data files.
4. Bring the data files online.
At this
point, the database is usable, and the data files are recovered. But, if you
want to put the data files back into their original location, proceed with the
following steps:
5. Create an image copy of the data files in
the original location using the BACKUP AS COPY command.
6. Take the data files offline.
7. Switch to the copy you made in step 5
using the SWITCH TO COPY command.
8. Recover the data files.
9. Bring the data files online.
You can
recover data files, tablespaces, tempfiles, or the entire database with this
command. The files being switched to must be image copies.
Using
SET NEWNAME for Switching Files
The SET
NEWNAME command can be used only inside a RUN block. It prepares a name mapping
for subsequent operations.
The SET
NEWNAME command defines the location where a restore operation of that data
file will be written. When the RESTORE command executes, the users01.dbf data
file is restored to /disk2/users01.dbf. It is written there, but the control
file is still not pointing to that location. The SWITCH command causes the
control file to be updated with the new location.
RUN
{
ALLOCATE CHANNEL dev1 DEVICE TYPE DISK;
ALLOCATE CHANNEL dev2 DEVICE TYPE sbt;
SQL "ALTER TABLESPACE users OFFLINE
IMMEDIATE";
SET NEWNAME FOR DATAFILE
'/disk1/oradata/prod/users01.dbf'
TO '/disk2/users01.dbf';
RESTORE TABLESPACE users;
SWITCH DATAFILE ALL;
RECOVER TABLESPACE users;
SQL "ALTER TABLESPACE users
ONLINE";
}
